1. Technical Field
The invention relates to fine patterning using exposure technology such as hologram, and particularly, to a method of aligning an exposure mask to an object subject to exposure, and a manufacturing method of a thin film element substrate using that method.
2. Related Art
In recent years, holographic technology of a Total Internal Reflection (TIR) type has been a focus of attention in a patterning process of a semiconductor device. This exposure technology employs a recording process of recording a desired pattern with respect to a hologram mask by using a hologram exposure device, and an exposure process of exposing a photoresist for semiconductor patterning by irradiating reproduced light to this hologram mask.
In the recording process, a recording beam of laser is first irradiated to a mask pattern (former reticule) corresponding to a pattern of the semiconductor device to cause refracted light to generate and to be emitted to a recording surface of a hologram mask. On the other hand, reference light is irradiated from a reverse side of the hologram mask at a fixed angle with respect to the recording surface of the hologram mask, causing to interfere with the refracted light from a former reticule. This enables an interfering pattern to generate on the recording surface of the hologram mask and to record it on the hologram recording surface.
In the exposure process, the hologram mask is placed at the same position of the former reticule, then an exposure beam which is reproduced light is irradiated from a direction opposite to the time of recording, while the refracted light which reproduced the former pattern on the photoresist is utilized for image formation thereby to expose the photoresist. Normally, in this exposure process, the hologram mask is such that by matching an alignment mark formed on the side of a substrate, which will become an object subject to exposure, to an alignment mark formed on the side of a hologram mask, alignment of the substrate to the hologram mask is carried out.
In case of carrying out patterning using a plurality of hologram masks, currently available procedures were to align the hologram masks to the substrate by using a substrate, on which alignment marks were respectively formed, to a position corresponding to each alignment mark formed on each of the plurality of hologram masks. Symposium of Image Display (SID) 03 Digest, P—40, pp. 350-353 is an example of related art.
However, there was a problem of a need of alignment marks corresponding to the number of hologram masks on the substrate side. This problem increases the number of alignment marks as the number of hologram masks used increased, as calling for a wide area on the substrate to form alignment marks.
While the alignment mark to be incorporated in such hologram mask for the hologram exposure device is prepared separately from a device area, it is necessary to set up a gap of some 5 mm with respect to the device area and the alignment marks for other hologram masks (other layers) (refer to FIG. 7 and FIG. 8).
FIGS. 7A and B are schematic plans respectively showing a first layer mask and a second layer mask which are original Cr-made masks (former reticules) for making masks for hologram. As shown in FIG. 7A, on a first layer mask 1 there are provided a first layer device area D1 located in a center and first layer alignment marks A1 at four corners. Further, as shown in FIG. 7B, on a second layer mask 2 there are provided a second layer device region D2 and second layer alignment marks A2 at the four corners. A1 and A2 have different mark patterns.
FIGS. 8A and B are schematic, structural drawings showing respective processes when recording the device area and when recording alignment marks at the hologram mask (second layer mask). As shown in FIG. 8A, when recording the device area, recording on the hologram mask is carried out by object beams through the device area D2 and reference beams through prisms, with four alignment marks A2 of an original Cr mask 2 in a condition of its shielding plates closed.
On the other hand, as shown in FIG. 8B, when recording the alignment marks, recording on the hologram mask is carried out by object beams through four alignment marks A2 of the original Cr mask 2, with the device area D2 in a condition of its shielding plate closed. On the hologram mask made herein, it is such that the mask is made with respective gaps of some 5 mm between the alignment marks and the device area. It should be noted that though not illustrated, in case of providing the alignment mark and alignment marks of other layers on the same mask, respective gaps of some 5 mm will be set up for providing them.
FIG. 9 is a schematic, structural drawing for explaining a method of aligning currently available exposure masks. As shown in FIG. 9, in a currently available case where there are many masks to be exposed such as a first layer mask (L1), a second layer mask (L2) . . . a seventh layer mask (L7), in view of necessity to maintain a minimum allowable gap between alignment marks on the same mask, alignment marks on the object such as a substrate, AL2-1, AL3-2, AL4-3, AL5-4, AL6-5, and AL7-6, with respective gaps of about 5 mm, are provided sequentially in the same placement direction for each alignment. It should be noted that in the drawing, masks are overlaid, one on top of the other, for the sake of explanation, whereas the actual alignment is carried out per mask between the upper layer side mark recorded on the hologram mask and the lower layer side mark recorded on the object. In such case where there are many masks to be exposed, an area, on which a device on the object can be prepared, significantly decreases in size.